The invention relates to a scanner for the acquisition of optical information, in particular of bar codes, having a laser device, a receiving device which detects laser light reflected from the surface, carrying the optical information of an object, and a measuring device, which registers the distance from the surface, carrying the optical information of the object, and emits a control signal corresponding to the distance.
Scanners of this type are known. They are used to identify objects which are provided with optical information. Only scanners having a laser device whose light beam is guided over the surface to be scanned by means of a suitable deflection device, in particular by means of a polygonal mirror, are discussed here. The scanners discussed here are used, in particular, to scan surfaces which are arranged at a greatly varying distance from the deflection device, for example in a distant range which varies by approximately 1 m. The depth of field of the reading range of an individual laser extends over a range of approximately 30 cm to 40 cm. If it is thus desired to cover a reading range of about 1 m with a scanner of the type discussed here, the laser device must comprise three laser light sources which each have a depth of field range of approximately 30 cm and are coordinated such that the reading or depth of field ranges supplement one another and thus provide a total distance range of about 1 m. In this case, for example, the first laser light source covers the first reading or scanning range from 0 cm to 40 cm, the second laser light source covers the second scanning region from 30 cm to 70 cm and the third laser light source covers the third scanning range from 60 cm to 100 cm. In practice, it has proved worthwhile for the ranges of the individual laser light sources to overlap somewhat, in order that an error-free signal is achieved as far as possible in all cases.
Scanners of the type discussed here are known whose deflection device has a polygonal mirror whose adjacent reflecting surfaces are each assigned to a specific laser light source, that is to say the scanner is controlled in such a way that the reflecting surface assigned to a laser is always exposed only to the laser light thereof. If an object is to be scanned in a specific reading or distance range, it is necessary to wait until, on the one hand, the laser light source assigned to this distance range is activated and the reflecting surface assigned to this light source is arranged in such a way that the laser light beam can be guided over the surface of the object to be scanned. Even with a very rapid succession of reflecting surfaces and a fast changeover of the laser light sources, waiting times arise until it is possible to scan an object at a specific distance from the corresponding laser light source. The effect of this is that the objects to be scanned can be guided past the scanner only at a restricted speed. This is disadvantageous particularly for the automatic scanning of objects, since the operating speed depends on the speed at which they are conveyed.
In order to eliminate this deficiency, it has been proposed to equip a scanner of the type described here, whose laser device has two or more laser light sources, with a measuring device which measures the distance from the object to be scanned and emits a corresponding control signal. With the aid of this control signal, the detection of the object is immediately followed by the activation of the laser which is suitable for the distance of the object. It is additionally provided that the light from all the laser light sources can be incident on any desired reflecting surface of the deflection device equipped with a polygonal mirror.
Scanners of this type manifest the disadvantage that a plurality of laser light sources must be provided for the purpose of acquiring optical information on objects situated in a distance range which is greater than the depth of field range of a laser. A scanner of this type is therefore relatively expensive and occupies a great deal of space, which often makes the structure of automatic acquisition systems considerably more expensive.